Ammonium nitrate gas generator composition



: temperature. temperature of 170 F. and conditionedfor 16 hours at this temperature. temperature and-permitted to-attain ambient temperature. he surface of the grain is then inspected visually and extremely severe test. as the ,vibration test to determine dimensional stability of This invention relates to ammonium nitrate compositions suitable for use as gas generating materials and particularly having propellant utility. More particularly the invention relates to an ammonium nitrate propellant capable of meeting military requirements for gas generator compositions.

Ammonium nitrate propellant compositions which are to be used for gas generation purposes, where the combustion gases drive a turbine or the like, must meet stringent military specifications. These gas generator grains are formed in a definite configuration determined by the burning time and commonly the space available for the gas generator cartridge.

Burning time is afiectedbythe amount of surface exposed for combustion. The presence of cracks and fissures abruptly introducesnew burning areas with a large increase in evolution of combus- 1 tion gases and erratic pressures in the gas generator hamb These cracks develop in storage, particularly with change in temperature of the grain. In order to dete rmi ne storage stability, gas generator grains are subjected to cycling tests. rapidly cooling the grain from ambient temperature to Roughly,t he cycling test involves -75' F; and conditioning the grain for 16hours at this The cold grain isthen rapidly raised to a The grain is then cooled to ambient by dye, treatment for the presence of cracks. A certain number of grains are fired as a final, check on themesence of internal cracks. In addition to. the cycling test on the. grain itself, the, complete gas generator with the grain imposition, is also cycled and. then fired. to test for the. presence of cracks. It can be seen that this is an Other tests are also imposed such the grain after severe handling. Also thereis a drop test in which the gas generator is dropped 6 ft. onto a concrete slab in order to test the strength of the case and the strength of the grain.

An object. of this: invention is an ammonium nitrate propellant composition which is suitable for military use United States Patent O in gas generators, particularly forthe driving of auxiliary turbines. Other objects will become apparent in the "course of the detailed description of the composition of the invention.

The. solid propellant composition of, theinyention consists of:

About, weight decompose.

gases, chemical solutions, oils and greases. an acnvated carbon made from a residual organic ma- 3,132,059 Patented May 5, 1964 The term ammonium nitrate as used in this specification and in the claims is intended to mean either C.P. grade or ordinary commercial grade ammonium nitrate or military grade. The particles may be coated with a small amount of moisture-resisting material such as petrolatum or paraffin. Finely ground ammonium nitrate is preferred.

The combustion catalyst utilized in the composition of the invention is an alkali metal salt of aminobenzoic acid. The sodium salt of ortho aminobenzoic is preferred. Hereinafter, the preferred salt is identified. by the trivial name, sodium anthranilate.

The composition of the invention includes in its content of oxidizable organic material, as a cooling material, an ammonium oxalate and preferably diammonium oxalate.

The composition of the invention includes an oxidizable material functioning as a stabilizer. This stabilizer is a salt of a nitrogen base and ethylene diamine tetraacetic acid (Versene). Illustrative examples of suitable nitrogen bases from which the salt may be made are ammonia (NH ammonium hydroxides; hydrazine; quaternary ammonium hydroxides, such as. tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, ethyl trimethyl ammonium hydroxide, and phenyl trimethyl ammonium hydroxide; the aliphatic amines, such as the primary, secondary and tertiary amines havingmethyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl' and hexyl radicals, e.g., methyl amine, methyl ethyl amine, triisopropyl amine; naphthenic amines, such ascyclohexyl amine (hexahydro, aniline); particularly those having 1-10 carbon atoms per molecule, the aromatic amines, such as phenyl amine (aniline), diphenyl amine, toluidine, xylidine, and mesidine; mixed aliphatic-aromatic amines, such, as phenyl methyl amine and tolyl' ethyl amine, wherein boththe aliphatic and aromatic radicals are joined directly to the nitrogen atom; and also mixed aliphatic-aromatic amines,

such as benzyl amine, where the aromatic nucleus is separated from the nitrogen atom by an alkyl group; heterocyclic amines, such as pyridine and. quinoline; and aliphatic, naphthenic and aromatic diamines, such as ethylene diamine, hexamethylene diamine and benzidine (4,4-biphenyl diamine). Ammonium hydroxide and hydrazine are particularly suitable nitrogen bases from which to form a salt of ethylene diamine tetraacetic acid. It is desirable that the salt used give a neutral or somewhat alkaline pI-I when dissolved in water.

The salts may be preapred. by mixing in an aqueous solution the aciclwith the desired nitrogen base, eyaporat ing the liquid therefrom, and drying the resulting salt. Evaporating and drying temperatures of. nothigher than about 300 F. are preferred, in order that the salt not The salts also may be prepared by reaction in an organic solvent, such as an alcohol, and filtering and drying the resultant precipitate.

The composition of the invention includes as a burning rateaccelerator finely divided carbon. The carbon component of the propellant composition includes finely divided, highly adsorptive activated carbons. These are well known in the art of decolorizing sugar and adsorption of gases. Examples of these are Norit and Nuchar, the former being a highly-adsorptive activated carbon usedv to adsorb odors, and to decolorize water, Nuchar is -terial obtained in the manufacture of cellulose and is characterized by high porosity resulting in high adsorptive capacity. Like Norit it is used as a decolorizing and dedorizing agent.

A second general class of carbons usefulfor increasing the burning rate of the propellant compositions are the carbon blacks. These are roughly classified as channel blacks prepared by the impingement of small natural gas flames, furnace combustion blacks produced by the partial combustion of essentially gaseous hydrocarbons in closed retolts and funace thermal blacks produced by thermal decomposition of hydocarbons such as acetylene in preheated furnaces. The carbon blacks are characterized by low ash content, by having extremely small particle size, that is, 50 to 5000 A., and contain adsorbed hydrogen and oxygen. Other carbon blacks which may be used in the propellant grains are lamp blacks produced by burning liquid fuels such as petroleum oils, tars and aromatic residues in specially designed pans, combustion taking place under restricted air supply conditions. The carbon blacks as indicated above are generally characterized by exceedingly small particle size, that is, well below #325 US. Standard sieve particle size. However,

to avoid dusting and convenience in handling, some carbon blacks are formed to the so-called bead type carbon blacks which beads are generally of such dimensions as to pass through a US. Standard sieve and are retained on a #200 US. Standard sieve. The beads are very soft and are physically unstable as beads and become disintegrated to smaller. than #325 U.S. Standard sieve during the mixing and milling of the composited propellant components as described hereinbelow. The carbon blacks are of low ash content, and usually contain less than 0.5% ash. Examples of head type carbon blacks are Micronex beads (channel blacks) and Statex beads (furnace blacks).

A third type of carbon which is useful for improving the burning rate of our gas-producing propellant composition is graphite, flake and amorphous. If derived from a natural graphite, the ash content should be reduced below about 5% which can be accomplished by treating the natural product by air flotation or the ash content may be reduced by leaching [with minenal acid or by other methods well known to the art. We prefer graphite of colloidal or semi-colloidal particle size.

Still another type of carbon which is suitable for increasing the burning rate of the gas-forming composition is finely ground petroleum coke, particularly petroleum cake obtained as a residue in the pipe-stilling of Mid-Continent heavy residuums. Such coke usually contains less than about 1% ash and is preferably pulverized to pass through a #325 US. Standard sieve prior to incorporation in the gas-producing propellant composition. The coke may be activated by methods well known to the art to improve the efficiency thereof as a burning rate promoter in our propellant composition.

Ammonium nitrate compositions in general tend to develop gas in storage at elevated temperatures. The composition of the invention includes a gassing inhibitor component. Aromatic amines when introduced into the ammonium nitrate based grain contain catalyst and finely divided carbon have the very desirable characteristic of decreasing the amount of gassing in high temperature storage and frequently even eliminating or essentially eliminating gassing for prolonged periods of time. The aromatic amine gassing inhibitors of this invention are illustrated by diphenylamine, dinaphthylamine and phenyl naphthylamine. In the case of the naphthyl amines, the

linkage between the naphthyl radical and the nitro gen may be either alpha or beta. Also those amines represented by the formula:

RZ(NRR")x In this formula Z is an aromatic nucleus selected from the class consisting of phenyl and naphthyl; R is selected from the class consisting of hydrogen and alkyl containing from 1 to 12 carbon atoms; R and R" are selected from the class consisting of hydrogen, and alkyl containing from 1 to 4 carbon atoms; and x is an integer from 1 Examples of monoamino-containing compounds are: aniline (monophenylamine, monoamino benzene), l-

4 naphthylamine, toluidine (methyl aniline) xylidine (dimethylaniline), dodecyl aniline, N-methyl aniline, N,N- dimethyl aniline, N-sec-butyl aniline.

Examples of the diamino compounds are: diamino benzene (phenylene diamine), diamino toluene (toluene diamine), diamino naphthylene, methyl diamino naphthylene, dodecyl diamino naphthylene, N-sec-butyl, diamino benzene, N,N'-di-sec-butyl diamino benzene, and N- methyl diamino naphthylene.

Examples of triarnino compounds are: triamino benzene, triamino naphthylene, triamino toluene, and triamino methyl naphthylene.

The composition of the invention may include one or more nonionic surfactants which tend to improve mixing of the composition and molding of shaped configurations. Any nonionic surfactant which is: inert to the other components of the composition is suitable for use in the composition. For purposes of illustration, the following broad classes of nonionic surfactants are set out hereinafter.

The surfactant polymers of alkylene oxides may be the polymers of ethylene oxide, copolymers of ethylene oxide and propylene oxide or block polymers of propylene oxide and ethylene oxide wherein ethylene oxide is added to polymers of propylene oxide. iIhese polyalkylene oxide condensation products are otherwise known as polyoxyalkylene glycols and have from two to three carbon atoms in the oxyalkylene unit.

One class of the polyoxyalkylene glycols which are effective are the commercial Pluronics which are polyoxypropylene-polyoxyethylene glycols or specifically, block copolymers. Pluronic L-6-2 has a molecular weight of about 2,000 of which 2,000 molecular weight from about 1500 to about 1800 is furnished by the propylene oxide units, the other alkylene oxide units in the polymer molecule being ethylene oxide units. The general formula for the Plunonics is Thus b in th s formula, for Pluronic L62 has a value of about 26 to about 31. Pluronic L-62 is a liquid having a viscosity at 25 C. of 300 to 500 centipoises.

As indicated hereinab'oye, derivatives of the polyoxyalkylene glycols are effective to reduce the consistency of the ammonium nitnate binder mixtures. Certain of these derivatives are the fatty alcohol monoethers and the fatty acid monoesters. An example of the monoether derivatives is Tergitol XC. Tergitol X0 is a monoether derivative of a copolymer of ethylene oxide and propylene oxide and has the approximate formula wherein R is an acylic hydrocarbon radical containing from 12 to 20 carbon atoms. The alkylene oxide constituents of the molecule each contribute about 1500' to give about 3000 to the total molecular weight, i.e., not more than about 3300, of the monoether derivative. In these ether derivative-type surfactant-s the number of ethylene oxide units may vary from about 22 to 35 and the number of propylene oxide units may vary from about 18 to about 27. The total molecular weight of these ethers will usually lie within the range of from about 2000 to about 3300.

An example of a monoester derivative of a polyoxyalkylene glycol which is effective is the commercial product Nonisol-250. This product is a mono-oleyl ester of polyoxyethylene having a molecular weight of about 1000. The fatty acid esters of polyoxyethylene sorbitol condensation products are effective surfactants for purpose of this invention. These may be produced by condensing ethylene oxide or polyoxyethylene with sorbitol followed 'by esterification of the condensation product with a 12 to 20 carbon atom fatty acid. In general, suitable products of this type have molecular weights within the range of from about 1000 to about 3300.

The term polyoxyalkylene glycol, ether and fatty acid ester derivatives thereof, as usedin this specification and claims includes (1) the polyethylene oxide homopolymers, copolymers of ethylene oxide and propylene oxide, block copolymerslof propylene oxide and ethylene oxide, said polymers haying a molecular. weight within the range of from about 1000. to about 3000, (2) the monoethei's of the polymers of (1). produced by. reacting fatty alcohols and; merc aptans. having 10 to 20 carbon atoms with poly.- mers of; (1 ethers having a molecular weight of about 2 .000 t oabeut 3300, and (3) 'moneesters of the polymers of (1') produced by esterification of said polymers with fatty acidshaving from 12 to. 20. carbon atoms per molecule, said mono'esters having molecular weights within thera e f ou .0 to 0 t 0- e e Y-ac used tQQesterify the condensation. product of'ethylene oxidewith sorbitol have from 12 to.20.carbon atoms, and the fatty acid esters produced. have molecular weights the range of irom about 1000.to.about 3,300. Particularly effective are the nonionic surfactants which maybe classified as esters of monoanhydro sorbit ols deseribedinUS. 2,398,193. These are known commercially as the. Span and Arlacel described on page 3 of br q m nt tl d At Surfaw A t v s t ti Suedin 1950. The sorbitans are mixtures oficyclized mongauhydrized sorbitol. The preferred Spa materials a 55 e compqsifige r e en ia l p al t rs 9t slats em and Q Q mop h ri e bit ns); derived from sorbitol, the sorbitan oleates being mixtures containing an average of from 1 to 3 oleyl radicals for each molecule of anhydrized sorbitol Sorbitol is dehydrated to give condensed link structures of sorbitans which, when esterified with oleic acid, produce the preferred Spans or Arlacels. Arlacel C, which is sorbitan sesquioleate, has been found to be particularly effective as an additive to promote ballistic dependability of the grain compositions. This material is an oily liquid at 25 C. having a specific gravity of 0.95-1.00, a flash point of about 450 F. and a fire point of about 530 F. Arlacel C has a viscosity at 25 C. of 900-4100 centipoises.

Another very effective nonionic surfactant is Span 85, which is a sorbitan trioleate having a viscosity at 25 C. of 100-250 centipoises. It has a specific gravity of 0.92- 0.98, a flash point of 500 F. and a fire point of 570 F.

The propellant includes as a temperature cycling aid a salt formed by the reaction of a nitrogen base and barbituric acid. Illustrative examples of suitable nitrogen bases from which the salt may be made are ammonia (NH ammonium hydroxides; hydrazine; quaternary ammonium hydroxides, such as tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, ethyl trimethyl ammonium hydroxide, and phenyl trimethyl ammonium hydroxide; the aliphatic amines, such as the primary, secondary and tertiary amines having methyl, ethyl, propyl, isopropyl,

butyl, isobutyl, pentyl and hexyl radicals, e.g., methyl amine, methyl ethyl amine, triisopropyl amine; naphthenic amines, such as cyclohexyl amine (hexahydroaniline); particularly those having l-10 carbon atoms per molecule,

. the aromatic amines, such as phenyl amine (aniline), di-

phenyl amine, toluidine, xylidine, and mesidine; mixed aliphatic-aromatic amines, such as phenyl methyl amine and tolyl ethyl amine, wherein both the aliphatic and aromatic radicals are joined directly to the nitrogen atom; and also mixed aliphatic-aromatic amines, such as benzyl amine, where the aromatic nucleus is separated from the nitrogen atom by an alkyl group; heterocyclic amines, such as pyridine and quinoline; and aliphatic, naphthenic and aromatic diamines, such as ethylene diamine, hexamethylene diamine and benzidine (4,4'-biphenyl diamine).

1 Ammonium hydroxide and hydrazine are particularly suitable nitrogen bases from which to form a salt of ethylene diamine tetraacetic acid. It is desirable that the salt used give a neutral or somewhat alkaline pH when dissolution. the acid with the desired, nitrogen base, evaporating. theliquid therefrom, anddrying the. resulting salt. Evaporating and drying temperatures of; not higher than about 300, are preferred, in order that the salt not decompose. I -he salts may also be prepared by reaction in an organic solvent, such as an alcohol, and filtering; and drying the resultant precipitant.

With the exception. of the hereinabove defined combustion. catalyst and the. ammonium nitrate, the other componentsrof the. composition; may, be. considered, as oxidizable. organic materials. Ina narrowersense, organic materials are. presentto function as a binder for the ammonium nitrate, catalyst and other solid. components. The binder material utilized in the instant composition consists of cellulose acetate, acetyl triethyl citrate. and dinitrophenoxyethanol.

Thefacetyl triethyl citrateis a well known plasticizer. The citrate may be the pure compound or commercial technicalgrade.

The dinitrophenoxyethanol component may be. essen-. tially pure material, or more usually will be' a mixture of one or more of the. dinitrophenoxyethanols. and a diether, e.g., bis-(dinitrophenoxykthanel In all cases, the dinitrophenoxyethanol is the predominant member and usually. will represent 65%, ormo re of this component. A mixture of 2,4wdinitrophenoxyethanol and 1,2-bis-.(2,4.- dinitrophenoxy)ethane is particularly. suitable. U.S. Patent No. 2,935,415 at columns Zand 3setsout a descrip: tion of classic methods of preparation of the. mixture of the two. materials and thespearation thereof. U.S. Patent No. 2,988,571 sets out a method of preparation of high purity dinitrophenoxyethanol.

The polymeric material present in the binder is cellulose acetate. Particularly suitable are the cellulose acetates which have combined acetic acid contents on the order of 50-58%. A preferred cellulose acetate is one made by the Celanese Company as grade LHFS 93, which has a combined acetic acid content of about 55%.

It has been discovered that the hereinabove defined nitrogen salts of barbituric acid are very effective in improving the temperature cycling characteristics of compositions similar to those set forth herein where the catalyst is derived from barbituric acid or parabanic acid or similar heterocyclic acids as well as with aminobenzoic acids or other catalysts based on benzene or naphthalene ring substituted with carboxyl groups and amino groups.

Examples Comparative tests were carried out on full size grains for particular gas generator applications. These full size grains were approximately 6.5" long and 5.5" in diameter and had a 1" longitudinal opening in the center of'the grain. The grains were restricted on the ends using a restrictor composed of cellulose acetate and acetyl triethyl citrate. Several batches of propellant were made for the tests and the mixing procedures were standardized to eliminate effects of differences of blending on the final result. Many of the tests needed for military specifications were performed, but only those pertinent to the temperature cycling ability of the grains are reported here.

The gas generator composition used in the tests as setting forth one embodiment in the composition of the invention had the following component content:

@ercent Component: by weight Cellulose acetate (Cellulose HLFS93) 9.4 Acetyl triethyl citrate 10.2 Dinitrophenoxyethanol (28% diether) 9.3 Sodium anthranilate 1.5 Carbon black 3.0 Ammonium oxalate 0.6 Diammonium Versenate 0.1 Toluene diamine 0.1 N-phenylmorpholine 0.8 Ammonium barbiturate 2.0

Ammonium nitrate (Spencer C.P.) 63.0

Twenty grains were temperature cycled, being enclosed in a plastic bag and subjected to temperature variation as described earlier in this specification. Each grain was inspected visually for surface cracks and also by a dye technique wherein a dye solution is applied to the surface of the grain and then wiped oli. The dye solution is adsorbed by the cracks; the presence of the dye solution is then determined by ultraviolet inspection of the surface of the grain. Grains which were not rejected for the presence of surface cracks were then test fired to determine the presence of interior cracks. In this particular series, 18 of the grains passed the temperature cycling test.

A number of grains were then prepared using the above component formulation except that no ammonium barbituate was present; the components were adjusted propionately to bring the composition to 100%. In a test of 30 of these grains, only 12 passed the temperature cycling test.

Other batches of grains were made changing the proportions of components, but still without ammonium barbituate. In all these other batches, the failures ran from 50% to as much as 100% of the grains tested.

Semi-commercial quantities of gas generator grains coming within the scope of the claimed composition show that the number of grains failing temperature cycling when produced in large mixers was less than 2% of the production, which percentage failure is completely acceptable for military requirements.

Thus having described the invention, what is claimed is:

1. A solid gas generator composition consisting of cellulose acetate, about 810%; acetyl triethyl citrate, about 8.5-11.5%; dinitrophenoxyethanol, about 810%; alkali metal aminobenzoate catalyst, about 1-2.5%; finely divided carbon, about 2-4%; ammonium oxalate, about 0.5-2%; stabilizer salt of a nitrogen base and ethylene diamine tetraacetic acid, about O.1-2.0%; aromatic hydrocarbon amine gassing inhibitor, about 0.l-0.5%; N phenylmorpholine, about 0.5l.5%; salt of a nitrogen base and barbituric acid, as a cycling aid, about 0.5-2.5%; a nonionic surfactant, about 0.0-0.3 and the remainder of said composition being essentially ammonium nitrate.

2. The composition of claim 1 wherein said gassing inhibitor is toluene diamine.

3. The composition of claim 1 wherein said stabilizer salt is diammonium ethylene diamine tetraacetate.

4. The composition of claim 1 wherein said cycling aid is ammonium barbiturate.

5. The composition of claim 1 wherein said catalyst is sodium anthranilate.

6. A solid composition consisting of cellulose acetate, about 9%; acetyl triethyl citrate, about 10%; dinitrophenoxyethanol, about 9%; sodium anthranilate, about 1.5%; carbon black, about 3%; diammonium oxalate, about 0.6%; diammonium versenate, about 0.1%; toluene diamine gassing inhibitor, about 0.1%; N-phenylmorpholine, about 0.6% ammonium barbiturate, about 2%; and the remainder of said composition being ammonium nitrate.

No references cited. 

1. A SOLID GAS GENERATOR COMPOSITION CONSISTING OF CELLULOSE ACETATE, ABOUT 8-10%; ACETYL TRIETHYL CITRATE, ABOUT 8.5-11.5%; DINITROPHENOXYETHANOL, ABOUT 8-10%; ALKALI METAL AMINOBENZOATE CATALYST, ABOUT 1-2.5%; FINELY DIVIDED CARBON, ABOUT 2-4%; AMMONIUM OXALATE, ABOUT 0.5-2%; STABILIZER SALT OF A NITROGEN BASE AND ETHYLENE DIAMINE TETRAACETIC ACID, ABOUT 0.1-2.0%; AROMATIC HYDROCARBON AMINE GASSING INHIBITOR, ABOUT 0.1-2.0%; AROMATIC HYDROCARBON AMINE GASSING INHIBITOR, ABOUT 0.1-0.5%; NPHENYLMORPHOLINE, ABOUT 0.5-1.5%; SALT OF A NITROGEN BASE AND BARBITURIC ACID, AS A CYCLING AID, ABOUT 0.5-2.5%; A NONIONIC SURFACTANT, ABOUT 0.0-0.3%; AND THE REMAINDER OF SAID COMPOSITION BEING ESSENTIALLY AMMONIUM NITRATE. 